1. Field of the Invention
The present invention relates to a system providing fresh air to the crankcase of an automotive type internal combustion engine suitable for operation on hydrogen fuel, regardless of whether hydrogen is actually employed in the engine.
2. Background Invention
Providing positive crankcase ventilation (PCV) for a hydrogen fueled engine is challenging to engine designers inasmuch as in the vent that oil mist is recirculated into the engine""s intake system, pre-ignition may occur. Because the most efficient system of operating a hydrogen-fueled engine without throttling, the task of controlling PCV flow is made more difficult due to the elimination of the pressure differential within the manifold, which usually results from the use of a throttle. The inventors of the present invention have determined that using one or more reed valves in combination with an intake venturi in certain cases, and a coalescing oil separator may be used to build a system which allows appropriate crankcase ventilation without concomitant introduction of lubricating oil into the engine cylinders.
It is noted above that the most efficient method of operating a hydrogen fueled internal combustion engine is without a throttle. Such engines may be operated at extremely lean air/fuel ratio conditions. A hydrogen-fueled engine will produce carbon-based emissions (HC, CO2) only as a result of the consumption of lubricating oil. As a result, oxidizing catalytic aftertreatment is not usually required with hydrogen fuel, provided oil consumption can be controlled. Unfortunately, hydrogen fueled engines may be subject to pre-ignition as a result of hot oil mist, oil residue or oil ash remaining in the combustion chamber from previous combustion cycles. This material may cause the fresh charge to auto-ignite before the normal spark ignition event takes place. And, hydrogen is especially prone to pre-ignition due its low ignition energy requirement.
When a hydrogen-fueled engine is operating in an unthrottled mode, almost no differential pressure exists between the intake manifold and the crankcase because the blow-by gas is to flow from the crankcase into the intake manifold so as to be consumed by the engine in a normal manner. Diesel engines have this characteristic but are not known to employ one-way reed valves to establish pressure differential.
In order to provide PCV flow, a combination of one or more reed valves, and. possibly an intake venturi, are incorporated, as shown in the figures. The reed valves utilize the dynamic pressure pulses there produced I the crankcase of all typical reciprocating internal combustion engines. These dynamic pressure pulses result from the non-harmonic piston motion that exists because the piston speed is faster in the upper half of the stroke than in the bottom half. As a result, even though an equal number of pistons are simultaneously ascending in their cylinders as are descending, a pressure wave is generated due to unequal piston velocity. The incorporation of reed valves at the crankcase outlet, or both the inlet or outlet, assures positive PCV flow. A high efficiency oil separator of a coalescing type is necessary to remove a maximum amount of oil mist particles even down to the micron size. The coalescing filter in turn collects liquid oil from the crankcase vapors back to the engine crankcase via a drain line with a check valve in the drain line, which prevents pulling crankcase oil out of the oil pan when the coalescing element becomes plugged.
A crankcase ventilation system for internal combustion engine includes a first valve for controlling air flow into the engine""s crankcase, a second valve for controlling air flow out of the engine""s crankcase, and a separator for receiving air flowing from the second valve and for removing oil entrained in the flowing air. A crankcase ventilation system according to claim 1 further includes a drain line for returning separated oil from the separator to the crankcase. A return line conducts air from the separator to an induction system associated with the engine. The first and second valves, which preferably comprise fast-acting valves such as reed valves, operate-so as to open and close at a frequency which approximates the frequency of air pressure waves occurring within the crankcase.
According to another aspect of the present invention, the air flow through the first described valve originates upstream of the flow restriction in the induction system, with a return line conducting air from the separator to a portion of the induction system which is downstream from said flow restriction in said induction system. Flow restriction may comprise a throttle.
According to yet another aspect of the present invention, the air flow through the first valve may originate upstream of a flow restriction in the induction system, with the return line conducting air from the separator to a first portion of the induction system which is downstream from the flow restriction, as well as to a second portion of the induction system which is upstream from the flow restriction. The upstream portion may comprise a venturi through which air is being inducted into the engine.
It is an advantage of the present invention that a crankcase ventilation system according to this invention allows the introduction of oil-free air to the induction system of an engine.
Other objects, features and advantages of.the present invention will become apparent to the reader of this specification.